Earth Satellite Radio Studies of the Ionosphere

Abstract

The first instance of the use of extraterrestrial radio sources to study the ionosphere occurred shortly after World War II, when Hey et al. (1946) noticed short period fluctuations in 64 MHz radiation from Cygnus. At first, these signal variations were attributed to fluctuations of the source, but subsequent correlation studies at spaced receiver sites suggested that their origin was in the earth’s atmosphere (Smith et al. 1950; Little 1952). Hewish (1952) pointed out that these “radio star” emanations could, in fact, be used to study the irregular nature of the ionosphere. Representative results from some of these early investigations of the ionosphere using radio stars are given in papers by: Parthasarathy et al. (1959), Little et al. (1962), Owren et al. (1964), and Fremouw (1966).